In a dye diffusion transfer recording system, a heat-sensitive transfer sheet (hereinafter simply also referred to as an ink sheet) containing a colorant (hereinafter also referred to as a dye) is superposed on a heat-sensitive transfer image-receiving sheet (hereinafter simply also referred to as an image-receiving sheet), and then the heat-sensitive transfer sheet is heated by a thermal head whose exothermic action is controlled by electric signals, in order to transfer the dyes contained in the heat-sensitive transfer sheet to the image-receiving sheet, thereby recording an image information. Three colors: cyan, magenta, and yellow, or four colors which consist of the three colors and black are used for recording a color image by overlapping one color to other, thereby enabling transferring and recording a color image having continuous gradation for color densities.
In recent years, as a result of the popularization of dye diffusion transfer recording-type systems and speeding-up of printing, those systems have been installed out of doors such as in amusement parks and tourist attractions, so that they have been used for an immediate printing purpose.
JP-A-2007-237617 (“JP-A” means unexamined published Japanese patent application) discloses a heat-sensitive transfer image-receiving sheet provided, on a heat insulation layer, with a receptor layer which contains a vinyl chloride-based latex and carnauba wax and utilizes an anionic fluorine-based compound.
JP-A-2009-83331 discloses a heat transfer image-receiving sheet provided with a receptor layer which contains a vinyl chloride-based latex and a polyether-modified silicone, and makes use of a nonionic surfactant.
However, a new problem occurred. That is, when images are printed out with the systems intended for the immediate printing in the outdoors as described above using these heat-sensitive transfer image-receiving sheets, a separation line occurs in black and high-density image areas.
This separation line (hereinafter, may also be referred to as sticking), which is one of failures occurring at the time of image formation, will be explained below.
In the dye diffusion transfer recording type systems, a heat-sensitive transfer sheet and a heat-sensitive transfer image-receiving sheet are superposed, and an image is formed. Since the image is formed on the heat-sensitive transfer image-receiving sheet, the heat-sensitive transfer sheet which has become unnecessary, needs to be peeled off without leaving any unnecessary matters or traces on the heat-sensitive image-receiving sheet.
However, as there is a demand for shortening the printing time, the temperature applied to the heat-sensitive transfer sheet upon recording tends to be set higher (and therefore, the heating time is shortened). Accordingly, the heat-sensitive transfer sheet and the heat-sensitive transfer image-receiving sheet do not peel off in succession, and there occur changes in the conveyance load, so that an image failure that leaves streak-shaped marks (separation lines) caused by peeling is prone to occur. Depending on the situation, the heat-sensitive transfer sheet partly fuses into the heat-sensitive transfer image-receiving sheet after printing.
Particularly when the printing environment is under high temperature and high humidity conditions, such as during the rainy season or in rainy weather in summer time, the separation lines are likely to occur, and when these failures are present in printed images, the defects may impair the image quality.
Thus, it has been strongly demanded to overcome these problems.